|Hay, El Hamidi|
|MACNEIL, MICHAEL - Delta G|
|CARDOSO, FERNANDO - Embrapa|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/2017
Publication Date: 9/1/2017
Citation: Hay, E.A., MacNeil, M., Cardoso, F. 2017. Genotype by environment interaction effects in genetic evaluation of preweaning gain for Line 1 Hereford cattle from Miles City, Montana. Journal of Animal Science. 95:3833-3838. https://doi.org/10.2527/jas2017.1829.
Interpretive Summary: Genetic evaluation is the foundation for beef producers to make permanent and cumulative improvement in their breeding stock. Year to year variation in environmental conditions greatly influences calf growth. It has long been held that the potential for breeding values and environments to interact and this interaction merits serious consideration in performance testing procedures, interregional exchange of seedstock, and sources of semen used for artificial insemination. The goal of this research was to determine if Line 1 Hereford cattle could have differing genetic evaluations for gain from birth to weaning depending on the year in which they were born. Estimates of effects of the calf’s genotype on its performance were found to vary depending on the environment as manifest by differences between years. Estimates of effects of the dam’s genotype, influencing the growth of her calf, were less sensitive to year-to-year variability. If the methods used in this study were implemented in genetic evaluations that are conducted by breed associations, then seedstock producers could tailor their choice of animals for breeding to the environment found on their farm or ranch, or that of their commercial customers. This level of customization could increase the rate of genetic gain as well as improve beef production efficiency.
Technical Abstract: That genotype by environment interaction potentially influences genetic evaluation of beef cattle has long been recognized. However, this recognition has largely been ignored in systems for national cattle evaluation. The objective of this investigation was to determine if direct and maternal genetic effects on preweaning gain would re-rank depending on an environmental gradient as determined by year effects. Data used were from the 76-year selection experiment with the Line 1 Hereford cattle raised at Miles City, Montana. The data were comprised of 7566 animals with a recorded phenotype and an additional 1862 ancestral records included in the pedigree. The presence of genotype by environment interaction was examined using reaction norms wherein year effects on preweaning gain were hypothesized to linearly influence the EBV. Estimates of heritability for direct and maternal effects, given the average environment, were 10 ± 2% and 26 ± 3% respectively. In an environment that is characterized by the 5th (95th) percentile of the distribution of year effects, the corresponding estimates of heritability were 18 ± 3% (22 ± 3%) and 30 ± 3% (30 ± 3%), respectively. Rank correlations of direct and maternal EBV appropriate to the 5th and 95th percentiles of the year effects were 0.67 and 0.92, respectively. In the average environment, the genetic trends were 255 ± 1 g/yr for direct effects and 557 ± 3 g/yr for maternal effects. In the 5th percentile environment the corresponding estimates of genetic trend were 271 ± 1 and 540 ± 3 g/yr, and in the 95th percentile environment they were 236 ± 1 and 578 ± 3 g/yr, respectively. Linear genetic trends in environmental sensitivity were observed for both the direct (-8.06•10-4 ± 0.49•10-4) and maternal (8.72•10-4 ± 0.43•10-4) effects. Thus, changing systems of national cattle evaluation to more fully account for potential genotype by environment interaction would improve the assessment of breeding stock, particularly for direct effects. Estimates of environmental sensitivity parameters could also facilitate identification of genetic limitations to production.